Screens that are used in rear-projection TVs are required to have the capabilities of improving viewing angle as well as diffusing and emitting incident light to raise the uniformity of the luminance (intensity) of emitted light. Recent years have seen the frequent use of video light realized by lasers that has high picture quality due to such characteristics as fixed wavelength and the ability to efficiently obtain linearly polarized light. The above-described diffusion capability is of particular importance because video light realized by laser has a high degree of straightness.
For example, FIG. 1 shows the configuration of a light-diffusing screen directed toward achieving uniformity of the luminance of emitted light that is disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2008-83687).
Screen 10 is made up by lenticular lens 11 and Fresnel lens 12. Light that is emitted from light source 70 is projected by way of projection lens 80, and this light is irradiated as incident light into Fresnel lens 12 that diffuses the incident light. The incident light that is irradiated into Fresnel lens 12 becomes scattered waves in which phase is shifted and scattered by the light-diffusing material in Fresnel lens 12, is emitted from Fresnel lens 12, and is irradiated into lenticular lens 11. The light that is irradiated into lenticular lens 11 is particularly distributed in a horizontal direction, whereby the emitted light (scattered waves) undergoes self-interference to produce uniform luminance.
The screen disclosed in Patent Document 1 employs a Fresnel lens provided with a diffusion characteristic and a lenticular lens that places light that is incident to the Fresnel lens in a uniform state. To further simplify the configuration, the same effect can be obtained by forming a lens array on the incident side.
In addition, in order to achieve a superior light diffusion characteristic and produce more emitted light than reflected light, a light-diffusing screen is proposed in which light-diffusing particles having two types of particle sizes are dispersed in a binder, and such a construction is disclosed in, for example, Patent Document 2 (Japanese Patent No. 4401681).
FIG. 2 shows the light diffusion characteristic of the light-diffusing screen disclosed in Patent Document 2.
FIG. 2(a) shows the light diffusion characteristic when incident light 202, that is generated by, for example, a lamp, is irradiated, and FIG. 2(b) shows the light diffusion characteristic when laser beam 205 is irradiated.
As shown in FIG. 2(a), the greater portion of incident light 202 that is irradiated into the light-diffusing screen becomes emitted light 203 that is scattered, and a portion becomes rear-surface reflected light 204. In FIG. 2, the length of the arrows of emitted light 203 and rear-surface reflected light 204 indicates the intensity of the light that is scattered in each direction. When light-diffusing particles are simply dispersed, the proportions of the emitted light and the rear-surface reflected light have substantially the same level, but dispersing light-diffusing particles having two types of particle size produces more emitted light 203 than rear-surface reflected light 204.
When laser beam 205 is irradiated, emitted light 206 becomes more abundant than rear-surface reflected light 207, as shown in FIG. 2(b).
FIG. 3 is a view for describing in greater detail the light diffusion characteristic when a laser beam is irradiated into a light-diffusing screen such as is disclosed in Patent Document 2.
As shown in FIG. 3(a), laser light from laser 301 is irradiated with angles of incidence of 0 degrees, 20 degrees, and 40 degrees into light-diffusing screen 302 having a viewing angle of 140 degrees, and the light intensity is then measured by brightness photometer 303 for the emitted light of each case. Brightness photometer 303 was moved in a circular arc over a range of from −70 degrees to 70 degrees in 5-degree increments.
FIG. 3(b) shows the results of the above-described measurement. Based on the high level of straightness of the laser beam, the intensity of scattered light is high in the direction along the direction in which the laser beam advances.
Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2010-145770) discloses a screen that, as a configuration for achieving a superior viewing angle characteristic and for providing wavelength selectivity to improve contrast, is provided with a layer in which micro-pieces having wavelength selectivity are dispersed and that scatters transmitted light.